This invention relates to densitometers, and more particularly to a specular reflectance microdensitometer for measuring and controlling the density of particles on a reflective surface.
One environment for use of such an instrument is in the field of xerography in which electroscopic toner particles are electrostatically applied imagewise to a photoconductive surface from which they are transferred to a support surface such as paper on which they are permanently fixed. For the sake of quality control it is desirable to monitor and control the amount of toner deposited on a xerographic surface prior to its transfer to a final support.
Reference is hereby made to U.S. Pat. No. 3,348,523, issued to Davidson and Pierce, the specification of which is incorporated herein by reference. The cited patent discloses a sensing device in a xerographic environment in the form of a photocell provided for receiving light rays reflected from a developed xerographic image. The light sensing device generates a signal in accordance with the relative density of the developed xerographic image and an associated electrical circuit provides feedback from the generated signal into the system to control the deposition of toner onto the surface.
It is an object of the invention to provide a specular reflection densitometer in which there is a substantially linear relationship between surface density and the output signal of the instrument.